ABSTRACT
Fabry-Pérot (F-P) [4-6], whispering-gallery (WG) [7-9], and 2D photonic crystal (PhC) [10-12] defect cavities are the common light-confinement mechanisms adopted for semiconductor lasers [13]. The optical path lengths of such cavities, dependent on the vertical heights of F-P cavities, or lateral dimensions of WG circular cavities and photonic bandgap (PBG) structures, are crucial factors determining the lasing characteristics. To confine propagating photons in controllable and predictable manner, these optical cavities are usually designed to be of the order of wavelength or even at sub-wavelength scales. Unlike conventional AlInGaP red laser diodes that can be processed by standard microlithographic techniques, the blue/UV cavities require further dimensional shrinkage in order to fulfill constraints associated with short-wavelength light confinement, so that traditional optical patterning techniques are no longer able to offer the required resolutions due to the diffraction limit. Although direct-write techniques such as electron-beam lithography (EBL) [14,15] and focused ion beam (FIB) [16,17] milling are capable of producing arbitrary 2D feature accurately down to the nanometer scale, they also each have their own drawbacks. High equipment cost, time-consuming point-by-point processing, and thus low throughput make large-volume manufacturing impractical.
